Writing instrument



FIG. 1 is a rear elevational view of a writing instrument showing my new design;

FIG. 2 is a left side elevational view;

FIG. 3 is a left front elevational view;

FIG. 4 is a left side elevational view;

FIG. 5 is a bottom plan view; and,

FIG. 6 is a top plan view thereof. 

The ornamental design for a writing instrument, as shown and described. 